CHARCOAL  AS  A  MEDIUM  OF  INHALATION. 
433 
it  on  a  filter,  that  no  free  iodine  was  contained  in  the  water, 
neither  could  I  detect  any  trace  of  iodic  acid,  or  any  combina- 
tion of  iodine  ;  but  on  the  addition  of  alcohol  to  the  well-drained 
charcoal,  a  densely  colored  solution  of  iodine  (proved  by  the 
usual  tests)  passed  through  the  filter.  M.  Bechi  is  therefore  in 
error  in  stating  that  alcohol  does  not  remove  it.  Although  the 
combination  with,  or  rather  retention  by  charcoal  is  powerful 
enough  to  prevent  the  abstraction  of  iodine  by  water,  still  it 
would  not  appear  sufficiently  so  to  cause  any  objection  to  its  em- 
ployment for  the  purpose  proposed,  should  this  be  thought  de- 
sirable, more  especially  as  M.  Magnes  has  shown  that  in  drying 
at  a  moderate  heat  in  presence  of  watery  vapor,  the  iodine  is  in 
great  part  given  off. 
It  is  of  course  necessary,  for  the  reason  before  stated,  to  use 
charcoal  free  from  alkalies,  alkaline  earths,  and  their  salts. 
The  employment  of  charcoal  respirators  has  given  rise  to  the 
objection — not,  I  think,  well  founded — that  the  charcoal  would 
by  use  become  deleterious,  owing  to  its  absorption  of  the  carbonic 
acid  given  off  from  the  lungs,  and  also  from  the  formation  of  this 
gas  by  the  oxidation  in  its  pores  of  the  volatile  carbonaceous  mat- 
ter, or  hydrocarbons,  given  off  in  small  quantities  from  the  same 
source.  To  determine  if  this  be  the  case,  I  took  a  certain  weight 
of  coarsely-grained  wood  charcoal,  placed  it  in  a  percolator,  the 
receiver  of  which  contained  a  solution  of  baryta  and  air  that  had 
previously  been  freed  from  carbonic  acid,  and  passed  a  consider- 
able quantity  of  cold  boiled  distilled  water  through  the  charcoal ; 
only  a  slight  turbidness  was  caused  ;  this  was  allowed  thoroughly 
to  deposit,  the  supernatant  liquor  withdrawn  by  means  of  a  sy- 
phon fixed  in  the  apparatus,  care  being  taken  to  admit  only  air 
free  from  carbonic  acid.  The  precipitate  was  twice  again  washed, 
allowed  to  settle,  and  the  water  withdrawn,  when  the  precipitate, 
thrown  on  a  filter,  dried  and  ignited,  gave,  (deducting  the  filter 
ash),  0-55  grains  of  residue.  A  similar  weight  of  charcoal  in 
respirators  was  worn  for  six  hours  by  three  healthy  individuals, 
and  treated  in  exactly  the  same  way  as  the  above  ;  the  residue 
obtained  was  only  0-33  grains,  or  somewhat  less  than  that  from 
the  charcoal  which  had  not  been  respired  through.  In  both  cases 
the  carbonate  of  baryta  contained  only  a  trace  of  sulphate.  An 
equal  proportion  of  charcoal,  heated  to  low  redness  and  cooled  in 
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